CN113725895B - Independent active support type photovoltaic inverter with unbalanced load - Google Patents
Independent active support type photovoltaic inverter with unbalanced load Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention provides an active support type photovoltaic inverter with unbalanced load. The independent active support type photovoltaic inverter with unbalanced load comprises: photovoltaic contacts, load contacts, a front-stage converter and a rear-stage inverter; the photovoltaic contact is used for connecting an external photovoltaic, and the load contact is used for connecting an external load; the first end of the front-stage converter is connected with the photovoltaic contact, and the second end of the front-stage converter is connected with the first end of the rear-stage inverter; the second end of the back-stage inverter is connected with the load contact. The invention can separate positive and negative sequences of voltage and current when the independent load operates, independently control positive sequence components and negative sequence components, control the positive sequence components to maintain busbar voltage and frequency by adopting a constant voltage constant frequency control strategy, introduce negative sequence double-loop control to inhibit the negative sequence components, eliminate power fluctuation, ensure stable operation of the system and improve operation reliability.
Description
Technical Field
The invention relates to the technical field of new energy power generation, in particular to an independent active support type photovoltaic inverter with unbalanced load.
Background
With the rapid development of human society, the traditional energy sources such as natural gas, petroleum and the like are gradually consumed, the resource shortage and the environmental problem caused by the energy sources are not ignored, the development and the utilization of new energy sources go on a history stage to become important issues which are not ignored in the whole world, and the development of the photovoltaic power source serving as one of the main modes of power supply of the new energy sources is paid attention to in all countries of the world. After the distributed energy is integrated into the power grid, a fixing response is generated to the power grid, high-efficiency grid connection can be realized through a reasonable control strategy, an active supporting effect on the power grid is achieved, and the running stability is improved.
When the power grid side fails, the distributed photovoltaic system needs to be separated from the power grid to carry out independent load, and the system is maintained to stably operate, so that the reliability is improved. When an actual power grid runs, an asymmetric three-phase load always exists, negative sequence components are generated in an inverter system, power fluctuation is generated, the output waveform of the inverter is seriously affected, meanwhile, negative sequence current can generate a certain negative sequence voltage drop in the line impedance, and the power quality is reduced. Photovoltaic inverters can be provided with the capability of independently carrying a three-phase unbalanced load, and can provide the voltage required for the operation of the load with high quality and stability. When the photovoltaic inverter is independently loaded, a voltage type control strategy is generally adopted, and when the loaded three phases are inconsistent, unbalanced current is generated, so that the output voltage is unbalanced, the negative load voltage is counteracted, and adverse effects are caused on the safe use of the load.
However, the photovoltaic inverter has a problem of poor power quality when operated independently under load.
Disclosure of Invention
The embodiment of the invention provides an independent active support type photovoltaic inverter with unbalanced load, which aims to solve the problem that the photovoltaic inverter has poor electric energy quality when running independently with load.
The embodiment of the invention provides an independent active support type photovoltaic inverter with unbalanced load, which comprises the following components:
photovoltaic contacts, load contacts, a front-stage converter and a rear-stage inverter;
the photovoltaic contact is connected with external photovoltaic, the load contact is connected with an external load, the first end of the front-stage converter is connected with the photovoltaic contact, the second end of the front-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining constant direct-current voltage of external photovoltaic;
and the back-stage inverter is used for separating positive and negative sequences of voltage and current and independently controlling the positive and negative sequences so as to eliminate unbalanced negative sequence voltage.
In one possible implementation, the pre-stage converter is a Boost converter;
the modulating signals of the Boost switching tube corresponding to the direct-current side capacitor voltage single closed-loop control by the Boost converter are as follows:
wherein u is dc_g Modulating the signal k for a Boost switch tube p_dc The value k of the proportional controller of the PI regulator i_dc Integrating the value of the controller for the PI regulator, u dcref For the given value of the capacitor voltage at the DC side, u dc Is the measured dc side capacitor voltage.
In one possible implementation, the post-stage inverter includes: positive and negative sequence separation module, A/D conversion module, positive sequence component control module, negative sequence component control module and D/A conversion module.
In one possible implementation, the calculation formula of the output value of the a/D conversion module is as follows:
wherein i is a 、i b 、i c Three-phase currents, i, respectively outputted by the inverter d 、i q U is the value of the output three-phase current in the Dq synchronous rotation coordinate system a 、u b 、u c Three-phase voltages output by the inverter, u d 、u q For the value of the output three-phase voltage under the Dq synchronous rotation coordinate system, theta 1 Is the angle between the d axis and the phase reference axis.
In one possible implementation, the D/a conversion module output value is calculated as follows:
wherein i is a 、i b 、i c Three-phase currents, i, respectively outputted by the inverter d 、i q U is the value of the output three-phase current in the Dq synchronous rotation coordinate system a 、u b 、u c Three-phase voltages output by the inverter, u d 、u q For the value of the output three-phase voltage under the Dq synchronous rotation coordinate system, theta 1 Is the angle between the d axis and the phase reference axis.
In one possible implementation manner, the positive and negative sequence separation module performs positive and negative sequence component separation of the voltage and current by adopting a time domain detection algorithm based on trigonometric function orthogonal transformation, and represents the voltage as a combination of positive sequence component and negative sequence component by utilizing the orthogonality of sine function and cosine function, and the calculation formula is as follows:
wherein a is 1 A is the positive sequence total component coefficient of voltage 2 Is the sine component coefficient of the negative sequence of the voltage, b 2 Is the cosine component coefficient of the negative sequence of the voltage, omega is the angular frequency of the voltage, phi 1 The phase angle is initialized for the positive sequence component of the voltage.
In one possible implementation manner, the positive sequence component control module controls the positive sequence component by adopting a voltage current double loop, and the negative sequence component control module comprises: the first voltage outer loop control module and the first current inner loop control module;
the negative sequence component control module adopts constant voltage and constant frequency to control the negative sequence component, and the positive sequence component control module comprises: the capacitor voltage equipartition control module, the outer loop control module of second voltage, the inner loop control module of second electric current and voltage feedforward module.
In one possible implementation, the calculation formula for generating the command value of the current inner loop control module by the first voltage outer loop control module is as follows:
wherein U is d_nref ＝0,U q_nref =0; wherein i is d_nref Is a negative sequence d-axis current instruction value, i q_nref Is a negative sequence q-axis current command value, k p_ndu Is the value k of the proportional controller of the negative-sequence d-axis voltage outer-loop PI regulator i_ndu Integrating the proportional controller value, k, for a negative sequence d-axis voltage outer loop PI regulator p_nqu External loop PI regulator ratio for negative sequence q-axis voltageValue of example controller, k i_nqu Integrating the controller value, U, for the negative sequence q-axis voltage outer loop PI regulator d_nref Is a negative sequence d-axis voltage command value, U q_nref Is a negative sequence q-axis voltage command value, U d_n And U q_n The values of the negative sequence voltages on the d axis and the q axis are respectively;
the calculation formula for generating the modulation signal by the first current inner loop control module is as follows:
wherein m is d_n And m q_n Respectively the d-axis negative sequence modulation quantity and the k-axis negative sequence modulation quantity of the output voltage of the inverter p_ndi 、k i_ndi The value of the proportional controller and the value of the integral controller of the negative-sequence d-axis voltage outer-loop PI regulator are respectively k p_nqi 、k i_nqi The values of the proportional controller and the integral controller of the negative sequence q-axis voltage outer loop PI regulator are respectively, I d_nref Is a negative sequence d-axis current instruction value, I q_nref Is a negative sequence q-axis current command value, i d_n And i q_n The values of the negative sequence current on the d-axis and q-axis, respectively.
In one possible implementation, the calculation formula for generating the command value of the current inner loop control module by the second voltage outer loop control module is as follows:
U d_pref ＝311,U q_pref ＝0
wherein I is d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, k p_pdu Is the value k of the proportional controller of the positive sequence d-axis voltage outer loop PI regulator i_pdu Integrating the value of the proportional controller, k, for a positive sequence d-axis voltage outer loop PI regulator p_pqu Is the value of the proportional controller, k of the positive sequence q-axis voltage outer loop PI regulator i_pqu Positive sequence q-axis voltage outer ringPI regulator integral controller value, U d_pref Is a positive sequence d-axis voltage command value, U q_pref Is a positive sequence q-axis voltage command value, U d_p And U q_p The values of the positive sequence voltages on the d axis and the q axis are respectively;
the calculation formula for generating the modulation signal by the second current inner loop control module is as follows:
wherein m is d_p1 And m q_p1 Generating modulation command values for positive-sequence d-axis current inner loops and positive-sequence q-axis current inner loops respectively, and k p_pdi 、k i_pdi The values of the proportional controller and the integral controller of the positive sequence d-axis voltage outer loop PI regulator are respectively k p_pqi 、k i_pqi The values of the proportional controller and the integral controller of the positive sequence q-axis voltage outer loop PI regulator are respectively, I d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, i d_p And i q_p The values of positive sequence current on d axis and q axis are respectively, K is the proportionality coefficient of feedforward signal, U d_p And U q_p The values of the positive sequence voltages on the d-axis and q-axis, respectively.
In one possible implementation, the method further includes: and the load contact is connected with the first end of the filter, and the second end of the filter is connected with an external load.
The embodiment of the invention provides an independent active support type photovoltaic inverter with unbalanced load, which comprises a photovoltaic contact, a load contact, a front-stage converter and a rear-stage inverter; the photovoltaic contact is used for connecting an external photovoltaic, and the load contact is used for connecting an external load; the first end of the front-stage converter is connected with the photovoltaic contact, and the second end of the front-stage converter is connected with the first end of the rear-stage inverter; the second end of the back-stage inverter is connected with the load contact; when the independent load is operated, positive and negative sequence separation is carried out on voltage and current, positive sequence components and negative sequence components are independently controlled, the constant voltage constant frequency control strategy is adopted to control the positive sequence components to maintain busbar voltage and frequency, negative sequence double-loop control is introduced to inhibit the negative sequence components, power fluctuation is eliminated, stable operation of the system is ensured, and operation reliability and electric energy quality are improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a block diagram of a two-stage photovoltaic independent band unbalanced load operation control provided by an embodiment of the present invention;
fig. 2 is a micro-grid structure diagram of off-grid switching provided by an embodiment of the present invention;
FIG. 3 is a block diagram of a negative sequence component voltage-current dual loop control provided by an embodiment of the present invention;
FIG. 4 is a block diagram of constant voltage and constant frequency control of a positive sequence component according to an embodiment of the present invention;
fig. 5 is a block diagram of voltage equalizing control of a capacitor at a dc side of an inverter according to an embodiment of the present invention;
fig. 6 is a waveform diagram of output voltage of a photovoltaic inverter without power quality control function according to an embodiment of the present invention;
fig. 7 is a waveform diagram of positive and negative sequence voltage output by an active support type photovoltaic inverter without power quality control function according to an embodiment of the present invention;
fig. 8 is a waveform diagram of an output voltage imbalance degree of an active support type photovoltaic inverter without a power quality control function according to an embodiment of the present invention;
fig. 9 is a waveform diagram of output voltage of an active support type photovoltaic inverter with an unbalanced load provided by an embodiment of the present invention;
fig. 10 is a waveform diagram of positive and negative sequence voltage output by an independent active support type photovoltaic inverter with unbalanced load according to an embodiment of the present invention;
fig. 11 is a waveform diagram of output voltage unbalance of an active support type photovoltaic inverter with an unbalanced load according to an embodiment of the present invention.
Detailed Description
In order to make the present solution better understood by those skilled in the art, the technical solution in the present solution embodiment will be clearly described below with reference to the accompanying drawings in the present solution embodiment, and it is obvious that the described embodiment is an embodiment of a part of the present solution, but not all embodiments. All other embodiments, based on the embodiments in this solution, which a person of ordinary skill in the art would obtain without inventive faculty, shall fall within the scope of protection of this solution.
The term "comprising" in the description of the present solution and the claims and in the above-mentioned figures, as well as any other variants, means "including but not limited to", intended to cover a non-exclusive inclusion, and not limited to only the examples listed herein. Furthermore, the terms "first" and "second," etc. are used for distinguishing between different objects and not for describing a particular sequential order.
The implementation of the invention is described in detail below with reference to the specific drawings:
fig. 1 is a schematic structural diagram of an active support type photovoltaic inverter with an unbalanced load. Referring to fig. 1, the independent unbalanced load active support type photovoltaic inverter includes:
photovoltaic contacts, load contacts, a front-stage converter and a rear-stage inverter;
the photovoltaic contact is connected with external photovoltaic, the load contact is connected with an external load, the first end of the front-stage converter is connected with the photovoltaic contact, the second end of the front-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining constant direct-current voltage of external photovoltaic;
and the back-stage inverter is used for carrying out positive and negative sequence separation on the voltage and the current and independently controlling the positive and negative sequences so as to eliminate the unbalanced voltage of the negative sequence, ensure the power supply of the positive sequence voltage to an off-grid external load and ensure the constant frequency voltage output by the photovoltaic inverter.
The invention discloses a specific control method of an independent active support type photovoltaic inverter with unbalanced load, which comprises the following steps:
step 1: the dc capacitor voltage is controlled by the pre-Boost converter.
Step 1-1: output capacitance voltage u of Boost converter dc With a given DC capacitor voltage reference u dc_ref And taking difference, sending the generated difference signal into a PI regulator to generate PWM modulation waves, wherein the calculation formula is as follows:
wherein u is dc_p Modulating the signal k for a Boost switch tube p_dc The value k of the proportional controller of the PI regulator i_dc Integrating the value of the controller for the PI regulator, u dcref For the given value of the capacitor voltage at the DC side, u dc Is the measured dc side capacitor voltage.
Step 1-2: the on/off of the switching tube in the boost circuit is controlled by the generated duty cycle signal.
Step 2: and the photovoltaic inverter is controlled by the rear-stage inverter part to output stable voltage to maintain the constant bus voltage frequency.
Step 2-1: the system bus voltage u abc And output inductor current i abc Through transformation, positive and negative sequence components U are obtained d_n 、U q_n And i d_n 、i q_n . The voltage (current) is expressed as a combination of positive and negative sequence components:
the subscript 1 represents a positive sequence component, the subscript 2 represents a negative sequence component, the positive sequence component is represented as the sum of a sine component and a cosine component for convenience in calculation, and the positive sequence component and the negative sequence component can be calculated by utilizing orthogonality of a sine function and the cosine function:
step 2-2: the voltage-current double-loop control negative sequence component is utilized, and the control block diagram is shown in fig. 3:
step 2-2-1: the voltage outer ring is utilized to generate a current inner ring command value, and the calculation formula is as follows:
wherein I is d_nref Is a negative sequence d-axis current instruction value, I q_nref Is a negative sequence q-axis current command value, k p_ndu Is the value k of the proportional controller of the negative-sequence d-axis voltage outer-loop PI regulator i_ndu Integrating the proportional controller value, k, for a negative sequence d-axis voltage outer loop PI regulator p_nqu For the value of the proportional controller, k, of the negative sequence q-axis voltage outer loop PI regulator i_nqu Integrating the controller value, U, for the negative sequence q-axis voltage outer loop PI regulator d_nref Is a negative sequence d-axis voltage command value, U q_nref Is a negative sequence q-axis voltage command value, U d_n And U q_n The values of the negative sequence voltages on the d-axis and q-axis, respectively.
Wherein,,
U d_nref ＝0,U q_nref ＝0 (5)
step 2-2-2: the current inner loop control module generates a modulation signal, and the calculation formula is as follows:
m is in d_n And m q_n Is the d-axis negative sequence modulation quantity, k of the output voltage of the inverter p_ndi 、k i_ndi The value of the proportional controller and the value of the integral controller of the negative-sequence d-axis voltage outer-loop PI regulator are respectively k p_nqi 、k i_nqi The values of the proportional controller and the integral controller of the negative sequence q-axis voltage outer loop PI regulator are respectively, I d_nref Is a negative sequence d-axis current instruction value, I q_nref Is a negative sequence q-axis current command value, i d_n And i q_n The values of the negative sequence current on the d-axis and q-axis, respectively.
Step 3: the positive sequence component is controlled by adopting a constant voltage constant frequency control strategy, voltage frequency support required by normal operation is provided for off-grid loads, and a control block diagram is shown in fig. 4:
step 3-1: the zero sequence current injection method is used for controlling capacitor voltage equalizing of the direct current side of the inverter, and the control block diagram is shown in fig. 5. The direct-current side capacitor voltage is subjected to difference, the voltage difference is sent to a PI regulator, and then the difference is performed with zero-sequence current components, so that an instruction signal is generated:
wherein m is p0 Respectively, the generated modulation signals, u 1 、u 2 Respectively the upper and lower capacitor voltages at the DC side, k p_pdc 、 k i_pdc The values of the proportional controller and the integral controller of the PI regulator are respectively, I 0 Is the zero sequence component of the current.
Step 3-2: the voltage outer ring is utilized to generate a current inner ring command value, and the calculation formula is as follows:
wherein:
U d_pref ＝311,U q_pref ＝0 (9)
wherein I is d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, k p_pdu Is the value k of the proportional controller of the positive sequence d-axis voltage outer loop PI regulator i_pdu Integrating the value of the proportional controller, k, for a positive sequence d-axis voltage outer loop PI regulator p_pqu Is the value of the proportional controller, k of the positive sequence q-axis voltage outer loop PI regulator i_pqu Integrating the controller value for the positive sequence q-axis voltage outer loop PI regulator, U d_pref Is a positive sequence d-axis voltage command value, U q_pref Is a positive sequence q-axis voltage command value, U d_p And U q_p The values of the positive sequence voltages on the d-axis and q-axis, respectively.
Step 3-3: the current inner loop control module is utilized to generate a modulation signal, and the calculation formula is as follows:
wherein m is d_p1 And m q_p1 Generating a modulation command value for the positive-sequence d-axis current inner loop, generating a modulation command value for the positive-sequence q-axis current inner loop, and k p_pdi 、k i_pdi The values of the proportional controller and the integral controller of the positive sequence d-axis voltage outer loop PI regulator are respectively k p_pqi 、k i_pqi The values of the proportional controller and the integral controller of the positive sequence q-axis voltage outer loop PI regulator are respectively, I d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, i d_p And i q_p The values of positive sequence current on d axis and q axis are respectively, K is the proportionality coefficient of feedforward signal, U d_p And U q_p The values of the positive sequence voltages on the d-axis and q-axis, respectively.
Step 3-4: let m d_p1 And m q_p1 Performing dq/abc inverse transformation to generate drive PWM signal, and adding DC bias modulation signal m p0 A positive sequence PWM signal is generated. A/D (i.e., abc/dq) and D/A (i.e., dq/abc) refers to switching between digital and analog circuits, where dq refers to the software portion.
Step 3-5: and superposing the positive sequence PWM signal and the negative sequence PWM signal to obtain an inverter switching tube driving PWM wave.
In order to test the invention, a simulation model of an independent active support type photovoltaic inverter with unbalanced load is built in MATLAB/Simulink.
Waveform diagrams of the photovoltaic inverter without the power quality control function with the three-phase unbalanced load are shown in fig. 6, 7 and 8. Fig. 6 is a waveform diagram of output voltage of a photovoltaic inverter without a power quality control function, fig. 7 is a waveform diagram of positive and negative sequence components of the output voltage, and fig. 8 is a waveform diagram of unbalance of the output voltage. As can be seen from comparison of the three waveform diagrams, when the three-phase load carried by the photovoltaic inverter without the power quality control function is unbalanced, the negative sequence component of the output voltage is larger, the voltage unbalance degree is higher, and the stable operation of the system is not facilitated.
Waveform diagrams of the case of the active support type photovoltaic inverter with an unbalanced load alone and a three-phase unbalanced load are shown in fig. 9, 10 and 11. Fig. 9 is a waveform diagram of output voltage of an active support type photovoltaic inverter with an unbalanced load, fig. 10 is a waveform diagram of positive and negative sequence components of the output voltage, and fig. 11 is a waveform diagram of unbalance of the output voltage. According to the control strategy, the negative sequence component of the output voltage of the photovoltaic inverter is greatly reduced, the three-phase unbalance of the voltage is very low, the electric energy quality of load voltage is ensured, and the reliability and stability of active supporting power supply of the photovoltaic inverter are improved.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (7)
1. An active support photovoltaic inverter independently with unbalanced load, comprising:
photovoltaic contacts, load contacts, a front-stage converter and a rear-stage inverter;
the photovoltaic contact is connected with external photovoltaic, the load contact is connected with an external load, the first end of the front-stage converter is connected with the photovoltaic contact, the second end of the front-stage converter is connected with the first end of the rear-stage inverter, and the second end of the rear-stage inverter is connected with the load contact;
the pre-stage converter is used for maintaining the direct-current voltage of the external photovoltaic constant;
the back-stage inverter is used for separating positive and negative sequences of voltage and current and independently controlling the positive and negative sequences so as to eliminate unbalanced negative sequence voltage;
the rear-stage inverter includes: the device comprises a positive and negative sequence separation module, an A/D conversion module, a positive sequence component control module, a negative sequence component control module and a D/A conversion module;
the positive and negative sequence separation module adopts a time domain detection algorithm based on trigonometric function orthogonal transformation to separate positive and negative sequence components of voltage and current, and uses orthogonality of sine function and cosine function to represent the voltage as a combination of positive sequence component and negative sequence component, and the calculation formula is as follows:
wherein a is 1 A is the positive sequence total component coefficient of voltage 2 Is the sine component coefficient of the negative sequence of the voltage, b 2 Is the cosine component coefficient of the negative sequence of the voltage, omega is the angular frequency of the voltage, phi 1 Initial phase angle for positive sequence component of voltage;
the positive sequence component control module adopts voltage and current double rings to control the positive sequence component, and the negative sequence component control module comprises: the first voltage outer loop control module and the first current inner loop control module;
the negative sequence component control module adopts constant voltage and constant frequency to control the negative sequence component, and the positive sequence component control module comprises: the capacitor voltage equipartition control module, the outer loop control module of second voltage, second electric current inner loop control module and voltage feedforward module.
2. The self-contained unbalanced-load active-support photovoltaic inverter of claim 1, wherein the pre-stage converter is a Boost converter;
the calculation formula of the modulation signal of the Boost switching tube corresponding to the direct-current side capacitor voltage single closed-loop control of the Boost converter is as follows:
wherein u is dc_g Modulating the signal k for a Boost switch tube p_dc The value k of the proportional controller of the PI regulator i_dc Integrating the value of the controller for the PI regulator, u dcref For the given value of the capacitor voltage at the DC side, u dc Is the measured dc side capacitor voltage.
3. The independent unbalanced-load active-support-type photovoltaic inverter of claim 1, wherein the a/D conversion module output value is calculated as follows:
wherein i is a 、i b 、i c Three-phase currents, i, respectively outputted by the inverter d 、i q U is the value of the output three-phase current in the Dq synchronous rotation coordinate system a 、u b 、u c Three-phase voltages output by the inverter, u d 、u q For the value of the output three-phase voltage under the Dq synchronous rotation coordinate system, theta 1 Is the angle between the d axis and the phase reference axis.
4. The independent unbalanced-load active-support-type photovoltaic inverter of claim 1, wherein the D/a conversion module output value is calculated as follows:
wherein i is a 、i b 、i c Three-phase power output by inverter respectivelyStreams, i d 、i q U is the value of the output three-phase current in the Dq synchronous rotation coordinate system a 、u b 、u c Three-phase voltages output by the inverter, u d 、u q For the value of the output three-phase voltage under the Dq synchronous rotation coordinate system, theta 1 Is the angle between the d axis and the phase reference axis.
5. The active support type photovoltaic inverter with unbalanced load according to claim 1, wherein the calculation formula of the command value of the current inner loop control module generated by the first voltage outer loop control module is as follows:
wherein U is d_nref ＝0,U q_nref =0; wherein i is d_nref Is a negative sequence d-axis current instruction value, i q_nref Is a negative sequence q-axis current command value, k p_ndu Is the value k of the proportional controller of the negative-sequence d-axis voltage outer-loop PI regulator i_ndu Integrating the proportional controller value, k, for a negative sequence d-axis voltage outer loop PI regulator p_nqu For the value of the proportional controller, k, of the negative sequence q-axis voltage outer loop PI regulator i_nqu Integrating the controller value, U, for the negative sequence q-axis voltage outer loop PI regulator d_nref Is a negative sequence d-axis voltage command value, U q_nref Is a negative sequence q-axis voltage command value, U d_n And U q_n The values of the negative sequence voltages on the d axis and the q axis are respectively;
the calculation formula for generating the modulation signal by the first current inner loop control module is as follows:
wherein m is d_n And m q_n Respectively the d-axis negative sequence modulation quantity and the k-axis negative sequence modulation quantity of the inverter output voltage and the q-axis negative sequence modulation quantity of the inverter output voltage p_ndi 、k i_ndi Respectively isNegative sequence d-axis voltage outer loop PI regulator proportional controller value and integral controller value, k p_nqi 、k i_nqi The values of the proportional controller and the integral controller of the negative sequence q-axis voltage outer loop PI regulator are respectively, I d_nref Is a negative sequence d-axis current instruction value, I q_nref Is a negative sequence q-axis current command value, i d_n And i q_n The values of the negative sequence current on the d-axis and q-axis, respectively.
6. The active support type photovoltaic inverter with unbalanced load according to claim 1, wherein the calculation formula of the command value of the current inner loop control module generated by the second voltage outer loop control module is as follows:
U d_pref ＝311,U q_pref ＝0
wherein I is d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, k p_pdu Is the value k of the proportional controller of the positive sequence d-axis voltage outer loop PI regulator i_pdu Integrating the value of the proportional controller, k, for a positive sequence d-axis voltage outer loop PI regulator p_pqu Is the value of the proportional controller, k of the positive sequence q-axis voltage outer loop PI regulator i_pqu Integrating the controller value for the positive sequence q-axis voltage outer loop PI regulator, U d_pref Is a positive sequence d-axis voltage command value, U q_pref Is a positive sequence q-axis voltage command value, U d_p And U q_p The values of the positive sequence voltages on the d axis and the q axis are respectively;
the calculation formula for generating the modulation signal by the second current inner loop control module is as follows:
wherein m is d_p1 And m q_p1 Respectively generating modulation command values for the positive sequence d-axis current inner loop,Generating modulation command value k by positive sequence q-axis current inner loop p_pdi 、k i_pdi The values of the proportional controller and the integral controller of the positive sequence d-axis voltage outer loop PI regulator are respectively k p_pqi 、k i_pqi The values of the proportional controller and the integral controller of the positive sequence q-axis voltage outer loop PI regulator are respectively, I d_pref Is a positive sequence d-axis current instruction value, I q_pref Is a positive sequence q-axis current command value, i d_p And i q_p The values of positive sequence current on d axis and q axis are respectively, K is the proportionality coefficient of feedforward signal, U d_p And U q_p The values of the positive sequence voltages on the d-axis and q-axis, respectively.
7. The self-contained unbalanced-load active-support photovoltaic inverter of any one of claims 1-6, further comprising: and the load contact is connected with the first end of the filter, and the second end of the filter is connected with the external load.
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